MicroRNAs (miRNAs), small (~22nt non-coding RNAs) function as sequence-specific post-transcriptional regulators of gene expression, by reducing target mRNA levels and/or inhibiting protein translation. Schratt et.al. (2006) have shown a link between miRNA function, neuronal spine development and the action of at least one growth factor that may play a role in neuroplasticity. Yet, little is known about miRNA expression patterns in the adult brain, or whether changes in miRNA expression occur following either acute or repeated drug use or whether any miRNA might underlie any known messenger RNA (or protein) changes known to occur following drugs use (or abuse). We hypothesize that miRNA expression alterations will be distinct across various stages of substance abuse and that drug exposure will result in distinctive miRNA expression patterns (anatomical and/or temporal) in two distinct groups of rodents selectively-bred based upon the novelty seeking trait (High Responders (HR) vs Low Responders (LR)), as these two groups of rodents have unique patterns of gene expression basally, after various types of challenges, and display individual differences in the propensity for substance abuse. In Aim 1, we will use laser capture microscopy to isolate specific brain regions known to be direct targets of cocaine and/or undergo drug-induced changes in synaptic plasticity prior to broad-scale miRNA profiling. We will use tissues derived from both HR and LR rodents under basal conditions; conditions where gene expression differences exist. miRNA expression differences will be validated by miRNA qPCR and spatial patterns of expression analyzed by miRNA in situ hybridization (ISH) methods. In aim two, we will use a cocaine sensitization paradigm (where drug exposure can be held constant) in both HR and LR rodents to examine miRNA regulation by cocaine at two time points (immediately following cocaine and following a period of abstinence) isolated and monitored as in aim 1. In aim 3, we will use cocaine self-administration procedures in HR and LR rodents, collect tissues at two time points (acute and abstinence) to examine miRNA regulation. In Aim 4, we will use antagomirs to block basal or cocaine regulated HR/LR miRNA differences to determine if miRNA blockade alters drug-induced behaviors. Together, these findings will shed light on whether miRNAs contribute to the initial propensity to seek drugs of abuse or play an important role in the induction and/or maintenance of cocaine addiction. PUBLIC HEALTH RELEVANCE: Our project evaluates small but novel genetic elements called microRNAs (miRNAs) that are thought to have broad influences on the types or amounts of proteins cells produce. In this proposal, we plan to examine whether there are miRNA changes in two different rodent lines that vary in their propensity to seek drugs under basal conditions. Further, we plan to examine in each rodent line how different miRNA levels vary in multiple brain regions as a function of cocaine use both acutely as well as long after the drug treatment has ceased. These findings will shed light on whether miRNAs contribute to the initial propensity to seek drugs of abuse or play an important role in the induction and/or maintenance of cocaine addiction.